Which of the following statements with regards to myelinated and unmyelinated axons is CORRECT? (1 mark)

Question

BlackTom AI · Accepted Answer

Voltage-gated Na+ channels are highly concentrated at the nodes of Ranvier in myelinated axons, while unmyelinated axons have Na+ channels distributed along the axolemma; myelin increases membrane resistance and decreases capacitance, enabling saltatory (jumping) conduction.

1) Relevant knowledge points and concepts
- Myelination: Schwann cells (PNS) or oligodendrocytes (CNS) wrap axons to form myelin sheaths. Internodal regions are insulated; nodes of Ranvier are small bare segments between sheaths.
- Channel distribution: In myelinated axons, voltage-gated Na+ channels are densely clustered at nodes of Ranvier; internodes have low channel density. In unmyelinated axons, Na+ (and K+) channels are more evenly distributed along the membrane.
- Propagation modes: Myelinated axons use saltatory conduction (action potentials regenerated at nodes), increasing conduction velocity. Unmyelinated axons use continuous propagation (sequential local depolarization along the membrane).
- Biophysical effects: Myelin raises membrane resistance (reduces current leak) and lowers capacitance (less charge needed to change membrane potential), both speeding conduction.

2) Step-by-step reasoning to evaluate options
- Check option (a): Claims clustering at nodes in both unmyelinated and myelinated axons. False—unmyelinated axons lack nodes and do not cluster channels at nodes.
- Check (b): Claims clustering in unmyelinated and even spread in myelinated. This is reversed from truth.
- Check (c): Claims even distribution in both. False—myelinated axons have node clustering.
- Check (d): Claims myelin plays no role in propagation differences. False—myelin is central to saltatory conduction and speed differences.

3) Calculations
- None required for this conceptual question.

4) Why the correct answer is correct
Because each of the specific statements (a–d) contradicts established facts about channel distribution and the role of myelin, none of them are correct. Therefore the only correct choice is "None of the above."

5) Why the other options are incorrect (brief)
- (a) Incorrect: unmyelinated axons do not have nodes and do not cluster Na+ channels at nodes.
- (b) Incorrect: reverses the true distributions.
- (c) Incorrect: ignores nodal clustering in myelinated axons.
- (d) Incorrect: ignores the critical biophysical changes (resistance/capacitance) produced by myelin that enable faster, saltatory conduction.

6) Conclusion
All four specific statements (a–d) are incorrect; thus option (e) None of the above is the correct answer. This matches the provided answer: e) None of the above.

Which of the following statements with regards to myelinated and unmyelinated axons is CORRECT? (1 mark)单项选择题

类似问题

Rapid conduction of action potentials around the nervous system is achieved in several ways, including:

When an axon is myelinated, one of the consequences is the redistribution of:

What is the primary function of the nodes of Ranvier in a myelinated neuron?

The Myelin sheath;

In __________ conduction, the impulse jumps from node of Ranvier to node of Ranvier.

In __________ conduction, the impulse jumps from node of Ranvier to node of Ranvier.

In a myelinated axon, the action potential _____ the segments of myelin, going from one node of Ranvier to the next.

更多留学生实用工具

智能学习助手

风格化写作助手

论文查重助手

文献引用助手

课堂转译助手

课堂笔记助手

Quiz搜索助手

学校历年真题

智能刷题助手

智能匹配练习

希望你的学习变得更简单